A systematic research has been conducted on the formation energy of point defects in MoS 2 by using a rigorous, transparent and dimensionally independent charged defect calculation theory TRSM model. The results show that the ionization levels of all n-type or p-type intrinsic defects in single-layer MoS 2 are very deep, with the S-vacancy (V S ) defect not the origin of n-type conductivity observed experimentally. On the contrary, the H atom adsorbed in MoS 2 has very low ionization energy, which may account for the n-type conductivity of MoS 2 .